The present invention relates to polishing particles each having a core-shell structure and a polishing agent including the polishing particles.
In the manufacture of semiconductor substrates each with an integrated circuit formed thereon based on the conventional technology, as irregularities or steps are generated on a silicon wafer when a circuit is formed With metal such as copper, and the metallic portions of the circuit are preferentially removed so that the steps on the wafer surface can be eliminated by polishing. When an aluminum wiring is formed on a silicon wafer and an oxide film made of, for instance, SiO2 as an insulating film is provided on the aluminum wiring, also irregularities due to the wiring are generated, and therefore the oxide film is polished fee in order to flatten it.
As a polishing method employed for the purposes as described above, the chemical mechanical polishing method (sometimes described as CMP hereinafter) is well known. In the method, a substrate with irregularities thereon is pressed to a rotating polishing pad, and the substrate itself is rotated and steeped into a polishing agent slurry together with the polishing pad. In this state, polishing particles included in the slurry are pressed because of the weight to the substrate having irregularities thereon, and as a result, the convex metallic portions of the substrate are removed and flattened. Further, for flattening a surface of an oxide film formed on a substrate, polishing is performed in a similar manner also for removing the irregularities of the insulating film (oxide film) formed on the circuit or for other purposes.
In this polishing step, spherical particles made of fumed alumina or fumed silica with the average particle diameter of about 200 nm are generally used as the polishing particles. As the polishing agent, an oxidizing agent such as hydrogen peroxide for improving the polishing rate for metal, benzotriazole (BTA) for suppressing corrosion or oxidization of metal, chemical polishing agents such as acids, or aqueous polishing agent slurry with a pH adjusting agent added therein are used together with the polishing particles as described above.
In polishing the substrates as described above, it is required that a surface of the substrate having been subjected to polishing is flat without any irregularity, step, or micro flaw, and further the polishing rate is required to be high. Further a degree of integration in the semiconductor materials has been becoming increasingly higher in association with the tendency for electric or electronic products with smaller size and higher performance, but if impurities remain, for instance, on a separation layer of a transistor, the required performance may not be achieved, or failures may occur. Especially when any alkali metal, especially Na is deposited on a surface of a polished semiconductor substrate or a polished oxide film, the alkali metal easily diffuses and is captured in defects of the oxide film or other sections, which may in turn result, when a circuit is formed on the semiconductor substrate, insulation fault or short circuit on the circuit with the dielectric constant dropped.
Because of the phenomena, the faults or failures may occur when the semiconductor substrate is used for a long period of time under the varying various conditions.
Japanese Patent Laid-open Publication No. HEI 11-302635 discloses, based on the finding that colloid including fine silica particles each covered with aluminum is more stable in the high alkali region as compared to the ordinary colloidal silica including the fine silica particles not covered with aluminum, use of a solution which is a colloid including fine silica particles each covered with aluminum and has a pH buffering activity and a high dielectric constant as a solution of a composition for polishing. Further the publication also includes the description that pH of the composition for polishing little changes in the high pH region and the polishing machining rate is high and stable.
The present invention was made to solve the problems as described above, and it is an object of the present invention to provide polishing particles making it possible to control a polishing rate by adjusting a thickness and/or density of a shell portion of polishing particles each having a core-shell structure for the purpose of solving the problems described above, and to provide a polishing agent including the polishing particles.
The polishing particles according to the present invention have a core-shell structure with an average particle diameter (D) in the range from 5 to 300 nm, and a shell portion of the polishing particles comprises silica with a thickness (ST) in the range from 1 to 50 nm.
A density of the shell portion is preferably in the range from 1.6 to 2.2 g/cc.
An Na content in the shell portion is preferably not more than 10 ppm.
A core portion preferably comprises one, two or more oxides selected from the group consisting of SiO2, Al2O3, ZrO2, SnO2, ZnO, CeO2, TiO2, and MnO.
The polishing agent according to the present invention comprises the polishing particles described above.